Despite the dramatic decline in the incidence of sudden infant death syndrome (SIDS) following worldwide education programs, SIDS remains the major cause of death in infants one to twelve months of age. Accurate, prospective identification of individual infants that are likely to succumb is not yet possible, though progress has been made in characterizing SIDS risk factors and pathogenesis. Further reduction in the incidence may be tied to a better understanding of the underlying mechanisms for SIDS. Numerous physiological differences have been related to body position and several hypotheses have been formulated to explain how these differences might render infants more vulnerable to SIDS. One prominent hypothesis relates SIDS to relative hyperthermia, thought to be caused by less efficient heat dissipation in the prone position. Despite 'normal' thermoregulatory adjustments in cardiorespiratory function, a small increase in body surface temperature of prone sleeping infants is known to persist. Sustained over time, mechanisms primarily designed to control body temperature might override the more fundamental metabolic control of gas exchange and lead to potentially destabilizing changes in oxygen and carbon dioxide stores. The thermally induced dissociation of cardiorespiratory function from the primary control of oxygen and carbon dioxide activity could, in turn, become lethal by altering normal ventilatory, circulatory, and arousal responses to additonal, normally innocuous environmental stresses. Our research proposal addresses the interactive relationships among body position during sleep, body temperature and cardiorespiratory and neuroelectric activity in the regulation of cardiovascular function during early development of low birth weight infants, as these infants are subsequently especially susceptible to SIDS. The overall objective of this proposal is to elucidate physiologic mechanisms that underlie SIDS and to develop age-appropriate, non-invasive tests that will identify infants who are at the greatest risk for SIDS. Lay Summary :The risk for SIDS, a major cause of early childhood death, cannot currently be predicted for individual babies. Knowing that sleeping prone and relatively warm versus supine and relatively cool increases the risk for SIDS we propose to compare the activity of the heart, lungs and brain at rest and under mild stress in both conditions. Our long term goal is to develop screening tests for infants at risk for SIDS. [unreadable] [unreadable] [unreadable]